6 Calculate the interaction energy of a point charge kj mol1

6. Calculate the interaction energy of a point charge (kj mol-1) with a point dipole when the charge is Na+ and = 1.85 D (H₂O) are separated by 0.35 nm. In water, six H₂O molecules coordinate to Na⁺ and stabilize the ion by solvation. Compare your result multiplied by six (ANS = -262 kJ/mol) to the hydration energy of Na⁺ (-406 kJ mol^-1).

Solution

Interaction energy of a point charge with a dipole is E = {- charge of ion. Dipole moment. Cos (angle between ion and dipole)} / {4. pi. permitivity of free space. (distance)²}

Putting these values E= {-1(1.85). 1}/ {4(3.142).8.854*10^-12 .(0.35nm)²} in this calculation the angle is considered to be zero. so that Cos(zero)=1